1. Field of the Invention
The present invention relates, in general, to a photoresist composition containing a compound capable of generating halogen radical when exposed to radiant light and, more particularly, to the use of a 4,6-bis(halomethyl)-s-triazine having diazophenyl group therein, which acts as a chromophore, thereby improving the photosensitivity and the surface condition of the patterns formed.
2. Description of the Prior Art
s-Triazine compound is known to generate halogen radical or acid when decomposed by radiant light, such as near uv and visible ray. It is useful for a plurality of purposes, particularly, including electronic material fields, such as chemical enhanced resist for semiconductor device memory, pigment-dispersing resist for liquid crystal display color filter, and dry film resist. Besides, s-triazine compound is added in a photoresist composition useful for facsimiles, copying and other picture forming systems. According to the purpose, such halogen radical- or acid-generating compound plays a role of radical photopolymerization initiator, acid-generating photopolymerization initiator, and photo-activator as acid catalyst.
Organic halogen compounds are decomposed by light to provide halogen radicals, such as chlorine and bromine. Since these halogen radicals have fast diffusion rates in photoresist composition in addition to being very active, photopolymerization efficiency is high when they react with vinyl groups containing double bond, allyl group, styryl group, acryl group or methacryl group, and cynamoyl group. Then, halogen radicals easily attract hydrogen atom from substrates, to generate hydrogen halides, which serve as acid donors, so that they can be used as an initiator for cation polymerization which reacts with vinyl ether group, epoxy group and styryl group. Also, halogen radicals lead to the conversion of functional groups present in bonding agents, serving as photo activators imparting functionality.
Well-known halogen radical-generating compounds include tetrachloro carbon, iodoform and tribromoacetephenone. These radical generators are decomposed by radiant light with very short wavelength. A photoresist composition which contains the halogen-generating compounds is sensitive to uv zone which is of shorter wavelength than those (300 nm to 450 nm) of typically used light sources. Thus, a significant problem of the halogen-generating compound is that it is difficult to generate radicals by radiant light.
In order to overcome these disadvantages, there were suggested halogen radical-generating compounds that have photosensitive zone ranging, in wavelength, from near uv to visible ray (300 nm-450 nm), a representative of which is halomethyl-s-triazine as illustrated in U.S. Pat. Nos. 3,954,475, 3,987,037, 4,189,323, 4,329,384, and 4,330,590. In spite of its ability to absorb the light of such wavelength zone, halomethyl-s-triazine has disadvantages in that the radical generation rate by photolysis and the photosensitivity of a photoresist composition comprising it both are relatively low.